1. Field of the Invention
The present invention is related to methods of isolating and purifying the valuable constituents from Crude Tall Oil (CTO) recovered from the black liquor residue of wood pulping processes, primarily used in making paper. More particularly, the present invention is related to methods of extraction of valuable constituents from the neutrals fraction of CTO. Most particularly, the present invention is related to methods of isolation and purification of extracted or distilled constituents of the neutrals fraction of CTO which, upon said purification and subsequent modification, are useful as a dietary supplement in foods to reduce cholesterol levels in humans.
2. Description of Related Art (Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98)
It has long been appreciated that the black liquor residue from wood pulping contains valuable chemicals, which make up the CTO, with various industrial applications. The black liquor contains the soaps of rosin and fatty acids, as well as sodium lignate and the spent cooking chemicals for reuse. The CTO is recovered by partially evaporating the black liquor, for concentration purposes, and then skimming off the tall oil soaps that float to the top of a skimming tank. The soap skimmings are converted to CTO by reaction with sulfuric acid and then separated from the simultaneously-formed spent acid by batch cooking, continuous centrifuging, or continuous decanting. The CTO is normally divided into various fractions by distillation which first extracts the pitch (or bottoms). The depitched CTO is then separated into fractions of heads, tall oil rosin (TOR), tall oil fatty acids (TOFA), and distilled tall oil (DTO). A major ingredient of the neutral fraction of CTO, concentrated in the pitch fraction thereof, is a class of compounds known as sterols, including .beta.-sitosterol. It is known, however, that a common place to obtain these sterols is via solvent extraction of tall oil soap, which is done commercially in Scandinavia.
Recently, U.S. Pat. No. 5,502,045 disclosed the use (by ingestion) of a sitostanol fatty acid ester for reducing serum cholesterol level. The patent's assignee, Raisio, a Finnish manufacturer of foodstuffs, grain, and specially chemicals, has developed a cholesterol-reducing margarine called Benecol.RTM.. The active ingredient (in cholesterol reduction) in Benecol.RTM. is the claimed fat-soluble stanol ester which prevents cholesterol from being absorbed into the human digestive system. The stanol ester is produced from plant-derived sterols (phytosterols) via hydrogenation and trans esterification reactions. Cholesterol reductions (LDL and HDL) of 10-15% are common for individuals with diets containing Benecol.RTM..
Therefore, the value of recovering plant-derived sterols has become enhanced and the particular problems associated with recovering sistosterol from tall oil pitch have become worthy of investigation. A viable commercial process must achieve a high percent recovery of neutrals and/or sterols (greater than 70% recovery is preferable) and achieve high final sterol purity (higher than 95% is desirable). Past attempts to extract neutrals/sterols from one or more fractions of CTO are reported in the following patents:
__________________________________________________________________________ Patent No. Inventor Title Issue Date __________________________________________________________________________ U.S. Pat. No. 2,499,430 Vogel et al. "Obtaining Sterols of High Purity" Mar 7, 1950 U.S. Pat. No. 2,530,809 Christenson et al. "Fractionation of Tall Oil" Nov 21, 1950 U.S. Pat. No. 2,530,810 Christensen, et al. "Separation of Unsaponifiabl e Matter Nov 21, 1950 from Tall Oil Residue" U.S. Pat. No. 2,547,208 Hasselstrom et al. "Method for the Refining of Tall Oil Apr 3, 1951 Residue" U.S. Pat. No. 2,715,638 Albrecht et al. "Production of Sterols from Tall Oil Aug 16, 1955 Pitch" U.S. Pat. No. 2,835,682 Steiner et al. "Sterol Recovery Process" May 20, 1958 U.S. Pat. No. 2,866,781 Chase et al. "Separating Non-acids from Soap Stocks" Dec 30, 1958 U.S. Pat. No. 2,866,797 Berry et al. "Improved Process of Isolating Sterols" Dec 30, 1958 U.S. Pat. No. 3,840,570 Julian et al. "Process for Preparing Sterols from Tall Oct 8, 1974 Oil Pitch" U.S. Pat. No. 3,879,431 Clark et al. "Purification of Sterols by Distillation" Apr 22, 1975 U.S. Pat. No. 3,965,085 Holmbom et al. "Method for Refining of Soaps Using Jun 22, 1976 Solvent Extraction" U.S. Pat. No. 4,044,031 Johansson et al. "Process for the Separation of Sterols" Aug 23, 1977 U.S. Pat. No. 4,124,607 Beaton et al. "Preparation of Sterol Substrates for Nov 7, 1978 Bioconversion" U.S. Pat. No. 4,420,427 Hamunen "Process for the Separation of Sterols Dec 13, 1983 or Mixtures of Sterols" U.S. Pat. No. 4,422,966 Amer "Separation of Neutrals from Tall Oil Soaps" Dec 27, 1983 U.S. Pat. No. 4,496,478 Kulkarni et al. "Process for Separating Unsaponifiables Jan 29, 1985 from Fatty and Rosin Acids" U.S. Pat. No. 4,524,024 Hughes "Processes of Recovering Fatty Acids Jun 18, 1985 and Sterols from Tall Oil Pitch" U.S. Pat. No. 4,849,112 Barder et al. "Adsorption Separation of Sterols from Jul 18, 1989 Tall Oil Pitch with Carbon Adsorbent" U.S. Pat. No. 4,935,168 Sjoberg et al. "Process for the Preparation of Alcohols" Jun 19, 1990 U.S. Pat. No. 5,097,012 Thies et al. "Solvent Extraction of Fatty Acid Stream Mar 17, 1992 with Liquid Water and Elevated Temperatures and Pressures" __________________________________________________________________________
These approaches have failed to provide both a high percent recovery of neutrals and/or sterols and a high final sterol purity. Recently, it was discovered that sterols could be isolated from the solvent extraction neutrals mixture from a tall oil pitch fraction using a direct precipitation process (described in commonly-owned application Ser. No. 09/115,003 filed on Jul. 1, 1998). Briefly, in the direct precipitation process, a small amount of methanol is added to the partially concentrated neutrals, the mixture is allowed to cool to 20-30.degree. C., and water is added to precipitate the sterols, again at 20-30.degree. C. However, this often results in precipitating very small crystals, which can present difficulties as the small crystals are filtered during the sterol isolation step. It is anticipated that generation of larger crystals not only would improve sterol filterability, but improved sterol yields and purity as well.
Therefore, it is an object of this invention to provide a method for recovering the solvent-extracted or distilled neutral fraction of saponified tall oil pitch and isolating a high percentage of the sterol component thereof, by treating the neutral fraction to isolate therefrom sterol crystals of enhanced size to result in improved sterol yields and purity.